Surface Charges on Current Carrying Conductors

Surface charges on current carrying conductors is a well known phenomenon though seldom talked about in the introductory courses. Besides, the charges are imperceptibly small making the phenomenon difficult to observe.

In this demonstration shown in class in Fall 2015, a couple of high voltage DC converters (EMCO) are used to generate a potential drop of around 20 KV about a piece of wire that has four or five 50 Mega-ohm resistors stringed together. A light and tiny piece of wrapped up aluminum foil is hung from a nylon thread. The foil touches one end of the circuit, picks up a charge (say negative). This negatively charged foil is subsequently repelled from the same end. This indicates the deposition of negative charge on the circuit’s end. Bringing this negatively charged foil to the opposite end of the circuit while make it momentarily stick. After sticking, the process of charge sharing and repulsion repeats at the positive end.